The Plugin Site (aptly named) has 111 free Photoshop-compatible plugins available for download.

Take your pick from categories such as Image Effects, Patterns/Textures, Photo Enhancement, and many more. Each plugin is rated according to a three-star usefulness scale; plus, you can easily see if the plugin is Mac or Windows compatible with the platform graphics. An excellent site for all you Photoshop aficionados out there. — Wendy Boswell